Sabtu, 10 April 2021

Earthquake of magnitude 6 strikes Celebes Sea, near Philippines - EMSC - Reuters

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(Reuters) - An earthquake of magnitude 6.0 struck in the ocean 214 km (132 miles) south-southwest of Sarangi, Philippines, the European- Mediterranean Seismological Centre said on Saturday.

The quake was at a depth of 300 km (186 miles), the EMSC said.

Reporting by Vishal Vivek in Bengaluru, Editing by William Maclean

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A pandemic problem no one has solved: Marine workers stuck at sea - Minneapolis Star Tribune

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Shipping-industry leaders are scrambling to solve the crisis of thousands of maritime workers who have been stranded because of the coronavirus pandemic. Global attention on the Suez Canal blockage last month gave them a new chance.

Unions, seafarer ministries and multinational ship owners and charterers — odd bedfellows in normal times — all seized the moment to raise awareness of the plight shipping workers face due to COVID-19 travel restrictions.

"We spend most of our time arguing with ship owners but the reality is on this one is we've really pulled together because it is a humanitarian crisis," said Stephen Cotton, general secretary of the International Transport Workers' Federation (ITF). "The irony of the Suez situation is one small incident generates enormous coverage."

As countries closed borders last March, many decided not to allow seafarers to get off ships at port. And the maritime workers who managed to get on land often weren't able to book plane tickets home because of other restrictions.

At the peak, about 400,000 maritime workers were unable to get off ships and get home, according to the International Chamber of Shipping. That number of workers struggling to repatriate now stands about 200,000.

Jan Dieleman, president of Cargill Inc.'s ocean transportation unit, took the opportunity in a recent Star Tribune interview to vent his frustration about the lack of interest in seafarers' well-being during the pandemic.

"Because they were not deemed essential workers, they've had to abide by every single country's laws like everybody else," Dieleman said. "Nobody has been able to solve this. Everyone is looking for someone to blame, but as an industry, as a society, we need to do better."

A complex patchwork of government rules limiting the cross-border movement of people continues to be a challenge, Cotton said. The growing prevalence of coronavirus variants is now leading to new lockdowns that could strand more workers at sea.

Compounding the issue, demand for shipping grew during the pandemic, said Jason Zuidema, executive director of the North American Maritime Ministry Association.

First came the surge in demand for personal protective equipment. Then came North American consumers and their online shopping that stressed the industry as their home, garden and office supplies filled containers floating aboard vessels from Asia to Los Angeles.

"[The companies] were still desperate to keep up the flow of essential goods and [personal protective equipment]," Zuidema said in an e-mail. "Keeping our store shelves stocked came at the expense of not allowing seafarers to go home for many additional months beyond the end of their contracts."

Three-month contracts turned to six months, six-month contracts turned into eight months. And even though 11 months is the longest amount of time a seafarer is supposed to be working aboard a ship, according to standards set by the International Labor Organization of the United Nations, there were cases of crew members unable to disembark for 17 months during the pandemic.

Cargill, which has between 1,400 and 1,500 seafarers working its chartered vessels, tried to redirect its ships to ports where crew changes were allowed, Dieleman said.

The shipping industry is filled with shadowy middlemen who aren't always held accountable, Cotton said. Many charterers refused to detour to crew-friendly ports, prioritizing on-time delivery of their cargo instead, he said.

And while some were stuck at sea, the restrictions put on crew changes meant other workers were unable to earn an income by not being able to board.

By mid-July 2020, 13 nations, including the United States, signed a joint statement acknowledging seafarers as key workers in the pandemic efforts and pledging to improve conditions for the workers.

The U.N. General Assembly in December adopted a resolution that all nations should extend that status to seafarers. The International Maritime Organization, the U.N.'s maritime agency, reported last month that less than 60 had done so.

"There is still a long way to go before we are back to a normal crew change regime," Kitack Lim, secretary-general of the IMO, said in a statement last month. "As vaccination is rolled out in many countries, I urge governments to prioritize seafarers in their national COVID-19 vaccination programs."

The shipping industry continues to press national governments on seafarer stranding and vaccination. More than 750 organizations signed the Neptune Declaration for Seafarer Wellbeing and Crew Change early this year.

"Seafarers should be recognized as essential workers by governments around the world," Zuidema said. "They need to get priority access to vaccines."

About a quarter of global seafarers who have so far responded to an ITF survey said they are considering leaving the industry after the negative experience of this past year.

"Some seafarers are reconsidering going back to sea," Cotton said. "How do you explain to your partner, children, parents that you don't know when you'll be home?"

Kristen Leigh Painter • 612-673-4767

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A pandemic problem no one has solved: Marine workers stuck at sea - Minneapolis Star Tribune

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Jumat, 09 April 2021

US Carrier Strike Group, Amphibious Warships Massed in South China Sea as Regional Tensions Simmer - USNI News - USNI News

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USS Makin Island (LHD-8) and the aircraft carrier USS Theodore Roosevelt (CVN-71) transit the South China Sea on April 9, 2021. US Navy Photo

A U.S. carrier strike group and amphibious ready group are in the South China Sea as tensions increase between Manilla and Beijing over a Chinese maritime militia incursion into the Philippines’ exclusive economic zone, the Navy announced on Friday.

The Theodore Roosevelt CSG and the Makin Island ARG – with the 15th Marine Expeditionary Unit embarked – are drilling in the South China Sea, according to U.S. 7th Fleet.

“Combining the capabilities of the carrier strike group with those of the Makin Island Amphibious Ready Group sharpens our tactical skills and demonstrates our continued dedication to the security and prosperity of the Indo-Pacific,” Rear Adm. Doug Verissimo, commander of Carrier Strike Group Nine, said in a Friday statement. “The combined Navy and Marine Corps team has been a stabilizing force in this region for more than a century and will continue to support all who share in the collective vision of peace, stability, and freedom of the seas.”

The exercises with the TR CSG and the three-ship ARG come as 44 Chinese maritime militia ships have remained massed off the coast of the Philippines in the vicinity of Whitsun Reef, Philippine officials said. Last month, 200 ships, identified by Chinese authorities as fishing vessels sheltering from bad weather, moved into the area around the reefs.

On Friday, Pentagon spokesman John Kirby said Defense Secretary Austin “remains concerned by the massing of Chinese maritime military vessels in the Union Bank area of the South China Sea and Chinese efforts of impeding the lawful rights of our treaty ally of the Philippines. The United States stands by our ally.”

The move of the U.S. ships into the region comes as officials in Manilla have raised alarms over Chinese behavior. This week a Philippines Department of National Defense spokesman said Manilla was in contact with Washington on the situation.

“We are continuously in talks with the U.S. on the matter of mutual defense,” Philippine defense spokesman Arsenio Andolong said in a statement reported by the Star Tribune newspaper in Manilla.
“Both parties are committed to undertake their obligations under the [1951] Mutual Defense Treaty so that neither stands alone in these issues involving the two states’ inherent right of self-defense.”

Late last month, Secretary of State Antony Blinken affirmed the U.S. commitment to defending the Philippines if it was attacked.

The “United States stands with our ally, the Philippines, in the face of the [People’s Republican of China]’s maritime militia amassing at [Whitsun Reef],” he said in late March.
“We will always stand by our allies and stand up for the rules-based international order.”

The maritime militia ships have been spotted operating with the China Coast Guard and People’s Liberation Army Navy ships.

Earlier this week, Philippine journalists approaching reefs in the South China Sea by boat were interdicted by two Type-22 Houbei PLAN catamarans.

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U.S. to send two warships to Black Sea, Russia voices concerns - Reuters

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ANKARA/MOSCOW (Reuters) - The United States will send two warships to the Black Sea next week, Turkey said on Friday as Russia, which has boosted its military forces near Ukraine, accused NATO powers that do not have a coast line in the region of increasing naval activity.

The Pentagon declined to discuss Turkey’s comments but said the military routinely sends ships to the region.

“That’s not anything new,” Pentagon spokesman John Kirby said in Washington, referring to U.S. military ships in the Black Sea.

Washington says Russia has amassed more troops on Ukraine’s eastern border than at any time since 2014, when it annexed Crimea from Ukraine and backed pro-Russian separatists in the eastern Donbass region of Ukraine.

Violence has flared between Ukrainian troops and the separatists. Russian President Vladimir Putin, during a telephone conversation with Turkey’s President Tayyip Erdogan, accused Ukraine on Friday of “dangerous provocative actions” in the Donbass region.

Turkey, a NATO ally, said on Friday the United States would deploy two warships to the Black Sea from April 14-15.

“A notice was sent to us 15 days ago via diplomatic channels that two U.S. warships would pass to the Black Sea, in line with the Montreux Convention. The ships will remain in the Black Sea until May 4,” Turkey’s foreign ministry said.

U.S. warships are regularly in the Black Sea, including a cruiser and destroyer being there late last month.

The 1936 Montreux accord gives Turkey control over the Bosphorus and Dardanelles straits, which connect the Mediterranean to the Black Sea. It also limits access of naval warships and governs foreign cargo ships.

Russian Deputy Foreign Minister Alexander Grushko raised concerns on Friday over what he said was increasing Black Sea naval activity by powers that did not have a coast line in the region, an apparent reference to the United States.

“The number of visits by NATO countries and the length of the stay of (their) warships have increased,” he was quoted as saying by the Interfax news agency.

According to a Reuters witness who keeps track of ships passing through Turkey’s Bosphorus strait, the United States and NATO increased their presence in the Black Sea early this year, when U.S. President Joe Biden’s administration took power.

The Reuters witness said the level had reached that seen in 2014-2015 at the time of the Crimea annexation.

Ukraine’s President Volodymyr Zelenskiy was due to meet Erdogan in Turkey on Saturday on a previously scheduled visit.

Reporting by Tuvan Gumrukcu, Ezgi Erkoyun, Yoruk Isik in Turkey and by Maria Tsvetkova and Polina Ivanova in Moscow and Idrees Ali and Phil Stewart in Washington; Writing by Tom Balmforth; Editing by Gareth Jones and Grant McCool

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Ocean eddies strongly affect global mean sea-level projections - Science Advances

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INTRODUCTION

Satellite-observed sea-level measurements indicate an ongoing increase in the global mean sea level since the satellite era (13). Global mean sea-level rise (GMSLR) threatens low-lying coastal regions, and these regions will benefit strongly from sea-level projections to adapt their coastal protection infrastructure (4, 5). Useful scenarios of future global mean sea-level change in the upcoming decades can only be made by state-of-the-art climate models. Current projections are based on climate models in which ocean-eddy processes are parameterized and the present-day state in these models strongly deviates from available observations, in particular, in the Southern Ocean (6, 7).

The climate models used in the fifth Intergovernmental Panel on Climate Change Assessment Report provide estimations of GMSLR in the upcoming decades (6). One of the greatest uncertainties at that time was the contribution by the Antarctic ice sheet (AIS) to GMSLR (8), and it was noted that marine ice-sheet instability of the West Antarctic ice sheet could change the GMSLR projections by several decimeters (9, 10). Since then, observational studies have shown that the Antarctic contribution to GMSLR is increasing over time, in particular, for western Antarctica due to basal melt near the grounding line of various ice shelfs and glaciers (1, 11, 12).

In a recent model study (7), 16 state-of-the-art AIS models subject to basal melt were used to determine the sea-level response by ice loss. Basal melt of ice shelfs was driven by subsurface ocean temperatures obtained from global climate model simulations within the Coupled Model Intercomparison Project phase 5 (CMIP5). However, the present-day state of the Southern Ocean and its responses to climate change strongly differ among the CMIP5 models (13, 14); this holds as well for the older CMIP phase 4 models (15, 16). Differences (e.g., temperature and salinity) in the mean state, compared to the available observations, have been attributed to the coarse horizontal (ocean model) resolution in these models (1719).

In ocean models with a higher spatial resolution, where eddies are partly represented, the present-day Southern Ocean surface temperature is much better represented compared to that in ocean models where eddies are parameterized (20). Explicitly representing eddies in one climate model also leads to substantially different regional dynamic sea-level projections for the Caribbean compared to version of the same model where eddies are parameterized (21). Motivated by these results, we here analyze GMSLR projections in two (noneddying and eddying) versions of the Community Earth System Model (CESM), taking into account Antarctic basal melt under a particular climate change scenario.

RESULTS

Climate model simulations

The CESM is a fully coupled state-of-the-art global climate model and is participating in the CMIP5 and CMIP6 efforts. The high-resolution version of CESM (HR-CESM) used here has an ocean component with a 10-km (0.1) horizontal resolution, capable of capturing the development and interaction of mesoscale ocean eddies (22), and an atmosphere component with a horizontal resolution of 50 km (0.5). Both the ocean and atmosphere component of the low-resolution version of the CESM (LR-CESM) have a horizontal resolution of 100 km (1). The ocean component of this low-resolution model cannot generate mesoscale ocean eddies. The high-resolution and the low-resolution versions of the CESM are spun up by 200 and 500 years, respectively, under a present-day (year 2000) forcing and then continued for 101 years under the same forcing to give the 101-year HR-CESM control and LR-CESM control simulations. The HR-CESM and LR-CESM simulations are initiated from the end of the corresponding spin up and are forced under a 1% pCO2 increase each year (model years 2000–2100). More details of the CESM simulations can be found in Materials and Methods. Both CESM versions have a volume conservation constraint for the ocean component and do not capture dynamical ice sheets. The contributions of the mass loss of glaciers and ice sheets to the GMSLR therefore need to be determined by postprocessing of the model results (see Materials and Methods). The CESM does not include any changes in the land-water storage.

Since observations of the Southern Ocean are limited, we compare the CESM control simulations results with one reanalysis product, the Mercator data, in which available observations are assimilated. Figure S1 (A, C, and D) shows the time mean (26 years) and depth-averaged (250 to 450 m) oceanic temperature fields for Mercator, HR-CESM control, and LR-CESM control, respectively. The depth range is based on the mean depth of the various Antarctic ice shelfs (7). The HR-CESM control is much better in agreement with reanalysis compared to the LR-CESM control. For example, the area-weighted correlation pattern [root mean square (RMS) deviation] over the 80S to 60S band is about 10% higher (45% lower) for the HR-CESM control compared to the LR-CESM control and is robust over the simulation period (fig. S1B). For the HR-CESM control, the largest temperature difference with respect from Mercator is found west of the Antarctic Peninsula with a magnitude of about −2C (fig. S1E). The LR-CESM control is warmer compared to Mercator in the Weddell Gyre and along the (eastern) Antarctic continental shelf (fig. S1F). The results in fig. S1 indicate that ocean subsurface temperature differences (with respect to Mercator) are reduced under a higher spatial resolution of the ocean model.

The RMS deviation is increasing over time, indicating that there is a slight drift in the control simulations (figs. S1B and S2, A and B). For the LR-CESM control, the temperature trends are persistent over the analyzed period. On the contrary, in the HR-CESM control, part of these (significant) trends is related to multidecadal variability in the Southern Ocean (23). This multidecadal variability is related to ocean-eddy interactions with the background flow (24), which are absent in the LR-CESM control.

Global mean sea-level rise

The GMSLR in the HR-CESM and LR-CESM simulations consists of four contributions, and these are shown over the 101-year period in Fig. 1 (A and B); details on the computation of each contribution can be found in Materials and Methods. The largest contribution to GMSLR is caused by (thermo)steric effects (adjusted for drift in each control simulation). The second largest and third (largest) contributions are related to melt by glaciers (fig. S3) and changes in the surface mass balance of the Greenland ice sheet (GrIS; fig. S4), respectively. These three contributions to GMSLR are fairly similar for both HR-CESM and LR-CESM (Fig. 1, A and B). The fourth contribution to GMSLR is due to changes in the surface mass balance and mass loss as a result of basal melt of the AIS (fig. S5). The Antarctic contribution strongly differs between the HR-CESM and the LR-CESM, where the LR-CESM projected value for Antarctica in the year 2100 is 9.3 cm higher compared to that of the HR-CESM. Note that the mass loss by basal melt is balanced by changes in surface mass balance in the HR-CESM (fig. S5A), resulting in a near-zero contribution for the AIS.

Fig. 1 Contributions to GMSLR.

(A and B) Contributions to global mean sea-level rise over the 101-year period for the HR-CESM and LR-CESM, respectively; the black curve indicates the total global mean sea-level rise. (C and D) The local sea-level difference between the time mean over years 2071–2100 and time mean over years 2000–2029 for the HR-CESM and LR-CESM, respectively.

The patterns of sea-level change between two 30-year periods (2071–2100 and 2000–2029) are shown for HR-CESM and LR-CESM in Fig. 1 (C and D), respectively. Here, gravitational, rotational, and deformation [GRD; (25)] effects by mass loss of glaciers and ice sheets are taken into account (see also figs. S3 to S5). Ocean currents change under global warming, affecting the dynamic sea level. The largest dynamic sea-level changes over time are found in the Southern Ocean and near western boundary currents for both HR-CESM and LR-CESM (fig. S6). Dynamic sea-level changes are also included in the local sea-level rise (Fig. 1, C and D) but do not contribute to GMSLR since the ocean has a volume conservation constraint.

The local sea level is projected to rise over the 2000–2100 period for most of the ocean surface in both simulations (Fig. 1, C and D). In the south of Greenland, the sea-level rise displays a dipole pattern of relatively higher and lower sea-level rise compared to the surroundings. This is associated with a weaker Atlantic meridional overturning circulation in both simulations (21), consistent with currently available observations (26, 27). The sea-level changes in the Southern Ocean are mostly caused by dynamic sea-level changes (fig. S6); however, these patterns differ substantially between the HR-CESM and LR-CESM. For example, there is a notable difference in the South Atlantic and Weddell Sea regions partly caused by the effects of ocean eddies on the path of the Agulhas Current (28). Agulhas Current changes (causing dynamic sea-level changes) contribute up to 60% of the local sea-level rise for the HR-CESM, and this is only up to 25% in the same region for the LR-CESM.

Antarctic basal melt

To further analyze the differences in Antarctic basal melt between LR-CESM and HR-CESM, we follow the procedure outlined in Levermann et al. (7) (see Materials and Methods). Positive oceanic temperature anomalies drive the basal melt of the ice sheets, which are shown here using five different regions in the Southern Ocean (Fig. 2A). For each region, we determined the vertically averaged subsurface temperature over a range of 100 m [for the specific depth ranges of the region, see table 1 in Levermann et al. (7)]. The time series for the five regions are shown in Fig. 2 (B to F) for the CESM simulations; also, the Mercator time mean and variability between 1993 and 2018 is plotted. The HR-CESM control reasonably matches with Mercator for the five different regions. On the contrary, the LR-CESM control is about 0.5 to 1.5C warmer compared to Mercator for the five different regions.

Fig. 2 Southern Ocean regions and temperatures in the CESM.

(A) The five Southern Ocean regions over which the basal melt is determined, similar to those in Levermann et al. (7). (B to F) Time evolution of the regional and depth-averaged oceanic temperature of the five Southern Ocean regions for the CESM simulations. For Mercator, the time mean over 1993–2018 is displayed (solid lines) and the shading indicates the minimum and maximum temperature over this period.

In the second half of the simulation, the LR-CESM temperature starts to deviate from the LR-CESM control temperature. In all regions (Fig. 2, B to F), a warming occurs over time (see also fig. S2D). Significant and positive (lag-)correlations are therefore found between the 2-m global mean surface temperature (GMST) anomaly and the five Southern Ocean regions for the LR-CESM (fig. S7), similar to the ones in Levermann et al. (7). The temperature anomalies are deviations from the respective control simulation (so not with respect to Mercator) and are adjusted for any drift (see Materials and Methods). For the HR-CESM, only East Antarctica and the Ross region (Fig. 2, B and C, and fig. S2C) are deviating from the HR-CESM control and for these two regions, significant (lag-)correlations exist with the GMST anomaly (fig. S7, A and B). There are no positive temperature anomalies (apart from natural variability) for the other three regions over the 101-year period for the HR-CESM and, hence, the lag-correlations with the GMST anomaly for these three regions are much smaller than those in the LR-CESM (fig. S7, C to E). The Southern Ocean subsurface temperature anomalies at the end of the century are positive for the LR-CESM and the largest anomalies are found in the southwestern part of the Weddell Sea (fig. S2D). On the contrary, the HR-CESM displays both positive and negative temperature anomalies in the Southern Ocean (fig. S2C). A nearly linear (positive) dependence of the GMST anomaly on the Southern Ocean temperature anomalies, a typical CMIP5 response (7), does not hold for the HR-CESM.

Most models participating in CMIP6 (see Materials and Methods) have the same horizontal ocean model resolution as the LR-CESM (i. e. ,1, see Table 1). There is a large variety in temperatures of the five Southern Ocean Regions for the CMIP6 ensemble, in particular, for the GMST, Ross region, and Amundsen region (fig. S8). Note that the CMIP6 control simulations cannot directly be compared to our CESM simulations because they have a preindustrial forcing. However, the temperature response of the CMIP6 simulations under the 1% CO2 increase scenario can be compared. The CMIP6 subsurface temperature anomalies (with respect to control simulations) of the last 30 years are shown in fig. S9 and are similar to the ones in fig. S2 (C and D). There is a large variety of temperature responses among the CMIP6 models, and the largest differences between the CMIP6 models are found near the Antarctic continental shelfs. The CMIP6 model mean has a positive temperature response over the whole Southern Ocean. The HR-CESM temperature anomaly pattern (fig. S2C) is most closely correlated with that of the GFDL-CM4 and CNRM-CM6-1-HR patterns, with a spatial correlation pattern value of r = 0.40 (Fig. 3A). The GFDL-CM4 and CNRM-CM6-1-HR have one of the highest horizontal ocean resolution (25 km) of the suite of CMIP6 models and are ocean-eddy permitting. Low correlation pattern values (∣r ∣ < 0.3) are found between the HR-CESM and most CMIP6 models and including the LR-CESM (Fig. 3A). The LR-CESM temperature pattern (fig. S2D) has great similarities with that of the CMIP6 CESM models (CESM2, CESM2-FV2, and CESM2-WACCM), and relatively high correlation pattern values (r = 0.64 to 0.72) are found between the LR-CESM and CMIP6 CESM models (Fig. 3B).

Table 1 Overview of the CESM and CMIP6 models and the spatial resolution of their ocean component lon, longitude; lat, latitude.
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Fig. 3 Southern Ocean temperature comparison with CMIP6.

(A) The area-weighted correlation pattern and RMS deviation between the HR-CESM temperature anomalies (fig. S2C) and those of the 31 CMIP6 models (fig. S9), as well as the LR-CESM (fig. S2D), between 80S and 60S. Before determining the correlation and RMS deviation, the HR-CESM pattern is interpolated onto each of the CMIP6 models native grid and the LR-CESM grid. (B) Similar to (A), but now, the LR-CESM is interpolated onto the CMIP6 models native grid and the HR-CESM grid. The CMIP6 models are categorized in four groups: the higher-resolution CMIP6 models (HR-CMIP6, nominal ocean model horizontal resolution < 100 km), the coarse-resolution CMIP6 models (CR-CMIP6, nominal resolution of 250 km), the CMIP6 CESM models (nominal resolution of 100 km), and the remaining CMIP6 models (nominal resolution of 100 km). Markers indicate the different models within each category.

The GMST is increasing for all CMIP6 models and the HR-CESM and LR-CESM responses are fairly similar to most of the CMIP6 models (fig. S10A). For East Antarctica (fig. S10B) and the Ross region (fig. S10C), the CESM simulations have a similar response to the CMIP6 models, but the anomalies are mainly below the CMIP6 mean. The HR-CESM hardly shows any positive temperature anomalies and is below the CMIP6 model mean for the Amundsen region (fig. S10D), Weddell region (fig. S10E), and the Antarctic Peninsula (fig. S10F). On the contrary, the LR-CESM is warming for these three regions, in particular, for the Weddell region and Antarctic Peninsula during the last 30 years of the simulation. The model mean of the five higher-resolution CMIP6 models (HR-CMIP6) tends to stay below the CMIP6 mean for the Amundsen region, Weddell region, and Antarctic Peninsula, similar to the HR-CESM. For the other two regions, the HR-CMIP6 remains close to the CMIP6 mean.

The temperature anomalies are converted to GMSLR equivalent by using response functions from ice-sheet models, which are subject to basal melt (7). The largest GMSLR as a result of basal melt from the five Southern Ocean regions is the Weddell region and this region also displays the largest spread among the CMIP6 models (Fig. 4). For each region, the GMSLR as a result of basal melt for the HR-CESM and LR-CESM is within the CMIP6 ensemble. However, the HR-CESM is below the CMIP6 mean for each region, which results in a total GMSLR contribution outside the CMIP6 ensemble band at the end of the simulation.

Fig. 4 GMSLR as a result of basal melt.

(A) Global mean sea-level rise as a result of basal melt of the AIS for the HR-CESM, LR-CESM, and CMIP6 models. (B to F) Global mean sea-level rise contribution from each of the five Southern Ocean regions (cf. Fig. 2A). Note that the vertical axes have different ranges.

The contribution as a result of basal melt to GMSLR (fig. S5, A and B, red curve) is partly compensated by an increase in snowfall over the AIS (fig. S5, A and B, blue curve). For the HR-CESM (LR-CESM), the AISs warm by a factor of 1.1 (1.3) with respect to the GMST anomaly and snowfall increases at 6.6%C−1 (6.2 %C−1) by Antarctic warming. These rates over the AISs are similar to the ones reported in the literature (29) (e.g., 1.1 ± 0.2 and 5.1 ± 1.5%C−1).

Recent observations (12) indicate that West Antarctica contributes 7.3 mm (55% of total AIS) to GMSLR between 1979 and 2017. Of this 7.3 mm, 6 mm (80%) originates from the Pine Island, Thwaites, and Crosson glaciers. These three glaciers are situated in the Amundsen region. For the HR-CESM and LR-CESM simulations (Fig. 4D), the GMSLR contribution of the Amundsen region is 5.3 and 4.4 mm in 101 years, respectively, which is considerably less compared to observations. In addition, the GMSLR contribution at the end of the simulation from the Weddell region is a factor 1.5, 18, and 3.4 higher compared to that of the Amundsen region for the HR-CESM, LR-CESM, and CMIP6 model mean, respectively. This demonstrates that either the GMSLR contribution by the Amundsen region is underestimated and/or that the GMSLR contribution by the Weddell region is overestimated by the different models.

The discrepancy between observations and models can be explained as follows. The temperature anomaly of the Amundsen region is not always representative for the temperature anomaly near the ice shelves where the basal melt occurs. The time-mean (model years 2071–2100) temperature anomaly of the Amundsen region is 0.08C and 0.15C for the HR-CESM and LR-CESM, respectively (fig. S10D). Over the same period, there are both positive (up to 1.1C) and negative (down to −1.0C) temperature anomalies in the Amundsen region for the HR-CESM (fig. S2C). For the LR-CESM, the temperature anomaly pattern in the Amundsen region is more homogeneous, and we find only positive temperature anomalies varying between 0.09C and 0.34C (fig. S2D).

In the ideal case, one would like to consider the subsurface temperature anomaly for each individual glaciers (e.g., the Pine Island, Thwaites, and Crosson glaciers). However, to resolve the ocean circulation near ice shelves, an even higher horizontal resolution is required [i.e., 200 m; (30)], which is about a factor 15 higher compared to that of the HR-CESM. Even if the temperature anomalies of each glacier is known, the corresponding response function is required and these are not available.

The relatively large GMSLR contribution of the Weddell region in the LR-CESM is due to model deficiencies (Fig. 3B). In all the low-resolution CESM simulations, strong positive temperature anomalies occur near the Weddell region (compare fig. S2D with fig. S9). These positive temperature anomalies in the Weddell region disappear in the HR-CESM (Fig. 3A).

Changes in the Southern Ocean circulation

To understand the difference between the temperature responses of HR-CESM and LR-CESM for the Weddell region and Antarctic Peninsula, the barotropic streamfunction (BSF), which measures changes in the vertically averaged circulation in the Southern Ocean, see Materials and Methods, is analyzed. The time-mean BSF fields (model years 2000–2029) of both simulations are shown in Fig. 5 (A and B). The large-scale pattern of the Antarctic circumpolar current (ACC) is represented in both simulations, as well as the Weddell Gyre and the Ross Gyre. The observed volume transport through Drake Passage is about 135 ± 10 sverdrup (Sv) (31, 32) (1 Sv ≡ 106 m3 s−1), while the modeled volume transport for the HR-CESM control with a time mean of 133 Sv (126 to 141 Sv, 101 years) is close to observations. The LR-CESM control has a much larger volume transport compared to observations with a time-mean value of 160 Sv (152 to 164 Sv, 101 years). It is well known that ocean eddies strongly affect the momentum balances in the Southern Ocean (33) determining the ACC strength.

Fig. 5 Changes in BSF and wind-stress curl in the Southern Ocean.

(A and B) Time mean over years 2000–2029 of the barotropic streamfunction (BSF) for the HR-CESM and LR-CESM. (C and D) Difference in BSF for the HR-CESM and LR-CESM between the time mean over years 2071–2100 and time mean over years 2000–2029. The gray and black contours show the zero wind-stress curl over (A and B) years 2000–2029 and (C and D) years 2071–2100, respectively (so not the difference over both periods), where 0ref indicates the time-mean over years 2000–2029. The wind-stress curl fields for the HR-CESM are smoothed by a Gaussian filter.

The difference between the time-mean BSF fields over the years 2071–2100 and the years 2000–2029 is shown in Fig. 5 (C and D) for both HR-CESM and LR-CESM, respectively. The LR-CESM displays an increase in the BSF values between latitudes of 80S to 60S and decreasing BSF values between latitudes of 60S to 40S, increasing the meridional BSF gradient and consequently increasing the ACC strength. For the HR-CESM, the increase in the meridional BSF gradient between these latitudes bands is small. However, there is an increase (more negative) in the meridional BSF gradient close to the Antarctic continent for the HR-CESM, which leads to an increase in the Antarctic Coastal Current (fig. S11, A and C). This current is poorly resolved (fig. S11) in the LR-CESM. The total westward volume transport of the Antarctic Coastal Current (near the Weddell Gyre) in the HR-CESM increases by about 10 Sv (compared to the HR-CESM control) in the last 20 years of the simulation (fig. S11E). This increase in westward transport is related to an intensification of the Weddell Gyre. The wind-stress curl is similar for the HR-CESM between the earlier and later period of the simulation (Fig. 5) and hence is not responsible for this intensification.

The modeled Antarctic sea-ice extent in the HR-CESM control and LR-CESM control reasonably matches with that of observations (1993–2018; see Materials and Methods) but is lower compared to observations (fig. S12, A and B). For example, in the HR-CESM control, LR-CESM control, and observations, the annual maximum sea-ice extent is ranging between 14.8 million and 18.3 million km2 (101 years), 13.9 million and 15.7 million km2 (101 years), and 18.6 million and 20.9 million km2 (26 years), respectively. In the HR-CESM, the sea ice is rapidly decreasing in the last 30 years of the simulation, especially in the Weddell Sea (fig. S12, A, C, and E). Less Antarctic sea ice results in more vorticity input by the wind and, from this, an intensification of the Weddell Gyre. The temporal intensification of the Weddell Gyre in the HR-CESM control (fig. S11E) is associated with Maud Rise polynya and Weddell polynya formation. These Maud Rise polynyas also form in the HR-CESM (around 3E, 65S in fig. S12C). There is no substantial sea-ice loss in the Weddell Sea and no polynya formation (23) for the LR-CESM (fig. S12, B, D, and F) and, hence, the Weddell Gyre strength does not increase (fig. S11, B, D, and F).

An increase in the Weddell Gyre strength will thermally isolate the Weddell region and the Antarctic Peninsula, similar to the ACC thermally isolating Antarctica from the lower latitude Southern Ocean. This explains the absence of subsurface warming for these two regions in the HR-CESM. For the LR-CESM, only the large-scale ocean circulation (i.e., ACC) is affected under climate change, but not the Weddell Gyre and Antarctic Coastal Current. Relatively, warm water from the Weddell Gyre is in this model advected toward the Weddell region and Antarctic Peninsula, leading to relatively large temperature changes there.

DISCUSSION

For the two different versions of the CESM (HR-CESM and LR-CESM), the overall responses to the increase in CO2 [GMST, contributions by glaciers to the GMSLR (34), thermo(steric) effects (21), and surface mass balance changes of the GrIS (35)] are quite similar and compare also well to 31 CMIP6 models analyzed. The projected temperature change and snowfall anomaly over the AIS for the HR-CESM and LR-CESM are also similar to the ones reported in Gregory and Huybrechts (29).

However, the Antarctic basal melt (7) strongly deviates between the HR-CESM and LR-CESM. The HR-CESM and LR-CESM simulations provide GMSLR projections of 5.4 ± 0.3 cm (95% confidence level) and 15 ± 0.8 cm (95% confidence level) through basal melt in 2100, respectively, which gives a factor 2.8 difference. The LR-CESM GMSLR projection of basal melt is within CMIP6 projections, but the HR-CESM projects quite lower GMSLR values with respect to CMIP6 ones. These differences in basal melt are related to the different horizontal resolutions in the ocean component of the models.

The Southern Ocean is a rather complex region where the large-scale ocean circulation, mesoscale ocean eddies, sea-ice formation, and atmospheric processes all play an important role in the response under global warming. Mesoscale ocean eddies are highly relevant for the redistribution and transport of heat and salt (20, 22, 36, 37) and are critical for the correct momentum balance for the large-scale circulation. Explicitly resolving ocean eddies in the HR-CESM does not only lead to a better representation of the present-day subsurface temperature distribution surrounding Antarctica (compared to LR-CESM) but also to a different response under global warming. For the HR-CESM, we find changes on both the large scale (e.g., in the ACC, sea-ice fields) and the regional scale (Weddell and Ross gyres and the Antarctic Coastal Current), while in the LR-CESM (and CMIP6 models), these occur only on the large scale.

Because of the extreme computational costs, there is unfortunately only one high-resolution simulation available for the analysis done here (HR-CESM control and HR-CESM). More of those simulations are required to provide a broader range of GMSLR projections, also under different climate change scenarios. However, the results here already indicate that sea-level projections based on low-resolution climate models should be interpreted with great care, in particular, regarding estimates of the effects Antarctic basal melt.

MATERIAL AND METHODS

Model output

The standard model output of the CESM simulations consists of monthly averaged oceanic fields of sea surface height above geoid [i.e., dynamic sea level (38)], horizontal velocity, temperature, and salinity. For the atmospheric component of the CESM, we analyzed the (near surface) air temperature and (solid) precipitation. Besides, we retained the Antarctic sea-ice fractions from the sea-ice component of the CESM. The HR-CESM and the LR-CESM are spun up by 200 and 500 years, respectively. All the CESM simulations lasted for 101 years. Most of the monthly averaged quantities are converted to yearly averages unless stated otherwise. Two additional LR-CESM simulations (not used) were branched off after a spin-up period of 200 and 1200 years, the latter is used in (21). The shorter spin-up period has an initial sea-ice distribution similar to the HR-CESM control. The drawback of this simulation is that the (subsurface) ocean fields are strongly drifting, and the trends are sometimes in the same order of the applied forcing. The HR-CESM control that has a spin-up period of also 200 years does not show these strong drifts in the ocean fields. A longer spin-up period of the LR-CESM (1200 years) displays hardly any drift in the ocean fields. However, in this LR-CESM control simulation, the sea ice is further equilibrated and the maximum sea-ice extent dropped from 12.8 million to 14.5 million km2 (model years 1200 to 1300). So, results from both additional simulations were not used here.

CMIP6 model output

We use results from the latest release of the CMIP6 and compare these to the output of our CESM simulations (Table 1). We analyzed the model output of the CMIP6 preindustrial control simulations and in which the atmospheric CO2 levels increase each year by 1%. We analyze the monthly averaged oceanic temperature (variable “theato”) fields and near surface air temperature (variable “tas”) fields of the first 101 model years, as is done for the CESM output.

Reanalysis (Mercator)

We retained model output from the Operational Mercator global ocean physical reanalysis product (http://marine.copernicus.eu/services-portfolio/access-to-products/). The ocean component of Mercator (i.e., NEMO) has a horizontal resolution of 1/12, 50 nonequidistant vertical levels, and covers the altimetry era (1993–2018). Mercator assimilates various observational datasets and the model is “steered” toward observations. We retained the monthly averaged temperature fields of the Mercator between 1993 and 2018.

Sea-ice observations

We obtained sea-ice measurements by the Scanning Multichannel Microwave Radiometer and Special Sensor Microwave Imager [http://nsidc.org/data/G02202, (39, 40)]. We retained the monthly averaged sea-ice fraction fields from the NASA Team algorithm with Goddard Quality Check. The sea-ice fraction fields are analyzed between 1993 and 2018, same as for the reanalysis.

Contributions by steric effects

The local steric contribution (ηS) is determined from postprocessing the model output (41). The contribution of both thermal effects and haline effects is determined as the full-depth integral over the specific volume anomaly (42)ηS=∫−H0ρ0−ρ(T,S,P)ρ0dz(1)

The temperature, salinity, and pressure dependency are taken into account while determining the density, and ρ0 = 1028 kg m−3. The steric contribution is expressed as an anomaly with respect to the initial value of the first model year. The globally averaged steric contribution, indicated by ηSg, is shown in Fig. 1, also known as the global mean thermosteric sea-level rise (38). We corrected for any drift in ηSg using the control simulations. After local ocean bottom pressure changes, the local thermosteric sea level eventually becomes ηSg.

Contributions by glaciers

To determine the contribution to GMSLR by the melt of glaciers, we followed the procedure outlined in Church et al. (34). First, the 2-m GMST is determined for the HR-CESM and LR-CESM. Second, we determined the GMST anomaly with respect to the control simulations (see below for determining the anomalies). The time integral of the GMST anomaly between 2000 – t [indicated by l(t)] is used to determine the GMSLR contribution by glaciersηglaciers(t)=fl(t)p(2)where f and p are constants, which are derived from four glacier models, and these values can be found in Church et al. (34) (their table 13.SM.2); negative values of l(t) are set to zero. For the uncertainty in the projections at time t, we take 20% of l(t) as the SD of a normal distribution. Third, we retained 2500 surrogate time series where a random number (independent of time) from the time dependent normal distribution is chosen. Last, we take the model mean over the four glaciers models, the percentile levels of ηglaciers are shown in fig. S3 (A and B).

Each of the 19 regions in the Randolph Glacier Inventory contribute to ηglaciers. Therefore, the contribution of each of the 19 regions to ηglaciers is scaled by its fraction of the global glacier volume. Here, we used the values in (43) of the modeled glacier volume in 2009 (their table 3), and we did not include the contribution of the glaciers in the Antarctic and sub-Antarctic region. The mass loss of each of the 19 glacier regions is multiplied by its fingerprint (due to GRD effects); the results are shown in fig. S3 (C and D). We used the 50% percentile level for ηglaciers in Fig. 1 and fig. S3 (C and D).

Contribution by the GrIS

Changes in the surface mass balance (ΔSMBGrIS) of the GrIS are governed by changes in snowfall and (surface) melt (35)ΔSMBGrIS=ΔSFGrIS−84.2ΔT600JJA−2.4(ΔT600JJA)2−1.6(ΔT600JJA)3(3)where ΔSFGrIS is the yearly snowfall anomaly over the GrIS and ΔT600JJA is the June to August temperature anomaly over the GrIS at 600 hPa. The anomalies are deviations from the control simulations (see below for determining the anomalies). The components of the surface mass balance are shown in fig. S4 (A and B). Negative values of ΔT600JJA are set to zero.

Ice dynamics and the positive melt-elevation feedback are not considered in relation (Eq. 3) because the GrIS topography is fixed (35). Following (34), the terms containing ΔT600JJA (melt terms) are multiplied by a factor E to adjust for the fixed GrIS topography. Here, E is a random chosen number from a uniform probability distribution in the range of 1.00 to 1.15 (time independent). Changes in ΔSMBGrIS are converted to GMSLR (factor of 361.8 Gt mm−1). The GMSLR by changes in the surface mass balance of the GrIS is shown in fig. S4 (C and D); here, we used 2500 surrogate time series for the percentile levels. The mass loss by the GrIS (using the 50% percentile) is multiplied by its fingerprint (due to GRD effects); the results are shown in Fig. 1 and fig. S4 (E and F).

Contribution by the AIS

Changes in the surface mass balance (ΔSMBAIS) of the AIS contribute to a negative GMSLR (29). We determined the snowfall anomaly (with respect to control simulation) over the AIS for the HR-CESM and LR-CESM. An increase in snowfall results in an increase in AIS dynamics (34) and the surface mass balance becomesΔSMBAIS=σΔSFAIS(4)where ΔSFAIS is the snowfall anomaly over the AIS and σ is a random number chosen from a uniform probability distribution in the range of 0.65 to 1 (time independent). We converted the ΔSMBAIS to GMSLR equivalent, and the 50% percentile from 2500 surrogates is shown in fig. S5 (blue curve).

Basal melt by increased oceanic temperatures on the continental shelfs surrounding Antarctica eventually leads to GMSLR (7). We followed the same procedure outlined in (7) and determined the vertically averaged temperature over the five Southern Ocean region (cf. Fig. 2A) for the CESM simulations (Fig. 2, B to F), and the vertical ranges for each region are provided in table 1 of Levermann et al. (7). Next, we determined the temperature anomaly (with respect to control simulation) for each region (indicated by ΔTO; fig. S10, B to F), and the basal melt Δm is defined asΔm(t)=βΔTO(t)(5)where β is the melt sensitivity parameter varying uniformly between 7 and 16 m yr−1∘C−1 (time independent).

Using the appropriate response function [indicate by R(t)] for each Southern Ocean region, the basal melt can be converted to GMSLRΣ(t)=∫0tm(t)R(t−τ)dτ(6)

The response functions are retained from 16 different ice-sheet models (7), and we used the last 101 years for each response function. For each ice-sheet model, we retained 2500 surrogates by varying β, and afterward, we determined the model mean of Σ(t) for the 16 ice-sheet models. The GMSLR as a consequence of basal melt (i.e., 50% percentile) is shown in fig. S5 (red curve), and the contribution for each region is shown in Fig. 4.

The mass gain or loss by the AIS (using the 50% percentile) is multiplied by its fingerprint (due to GRD effects). For the increased snowfall anomaly, we used the fingerprint of the entire AIS. GMSLR as a result of basal melt at the East Antarctic region, half of the Ross region, and half of the Weddell region is multiplied by the fingerprint of East Antarctica. We included half of the GMSLR contribution of the Ross region and Weddell region since both regions consist of an eastern region and western region (12). The GMSLR contributions of the remaining regions (i.e., Amundsen region, Antarctic Peninsula, half of the Ross region, and half of the Weddell region) are multiplied by the fingerprint of West Antarctica. The final fingerprints of the AIS are shown in fig. S5 (C and D).

Dynamic sea-level changes

The sea surface height above geoid (variable “SSH”) is part of the standard output of the CESM, referred to as the dynamic sea level (38). The globally averaged dynamic sea level is about zero since the CESM has a volume constraint for the ocean and does not contribute to GMSLR; we uniformly removed the global mean from the dynamic sea-level fields. Local dynamic sea-level changes are shown in fig. S6 for the HR-CESM and LR-CESM.

Determining anomalies (e.g., of temperature)

The (depth-averaged) temperature anomalies are determined with respect to the control simulations. However, some of the temperature fields display a (significant) drift in the control simulations (fig. S2, A and B). First, we determined the linear trend (αC) of a time series (yC) in the control simulation. This linear trend was subtracted from the relevant time series (y˜=y−αC) and the control time series (yC˜=yC−αC). Next, the time mean of the detrended control simulation (yC¯) was subtracted to retain the anomalies (y′=y∼−yC¯). This procedure was applied to all temperature time series, as well as for the snowfall time series.

Area-weighted correlation coefficient and RMS deviation

First, we determined the area-weighted temperature between 80S and 60S of two climate models, indicated by T¯1 and T¯2. Next, the area-weighted covariance is determined using the following expressioncov(T1,T2)=∑iAi(Ti1−T¯1)(Ti2−T¯2)(7)where Ai is the normalized area of a grid cell i with respect to the total area A. The area-weighted correlation coefficient, r, becomesr=cov(T1,T2)cov(T1,T1)cov(T2,T2)(8)

In a similar way, the area-weighted RMS deviation can be determined usingRMS=∑iAi(Ti1−Ti2)2(9)

For the HR-CESM and LR-CESM, we interpolated the temperature fields onto the Mercator grid and the CMIP6 native grids before determining r and RMS.

Barotropic streamfunction

The barotropic flow is defined as the full-depth integral of the horizontal velocityBF→=∫−H0ν→ dz(10)

Starting from Antarctica (with a value of 0 for the BSF), we integrate the zonal component of the barotropic flow (indicated by BFx) meridionally to determine the BSFBSF(x,y,t)=∫90∘SyBFx(x,y′,t)dy′(11)

For convenience, the average value of the BSF along the African coast line is subtracted from the entire BSF field.

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April 10, 2021 at 01:02AM
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Japan to Announce Fukushima Water Release Into Sea Soon - U.S. News & World Report

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[unable to retrieve full-text content]Japan to Announce Fukushima Water Release Into Sea Soon  U.S. News & World Report The Link Lonk


April 09, 2021 at 08:50PM
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Sea Turtle Inc. ‘not concerned’ about SpaceX activities - KXAN.com

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SOUTH PADRE ISLAND, Texas (KVEO) — SpaceX’s goals of sending people to Mars aboard the Starship rocket are still in the early trials, often with fiery endings that send debris in all directions. Leading some to wonder if wildlife in the area is impacted by the debris.

The beaches of South Texas and Northern Mexico are home to the rarest, most critically endangered sea turtle on the planet: the Kemp’s ridley sea turtle.

Kemp’s ridley sea turtles have been on the endangered species list since the 1970s, and where Kemp’s ridley sea turtles lay their eggs is very important.

“Our beaches here, South Padre as well as Boca Chica beach, both of these are very important to nesting females, and to nesting Kemp’s ridleys. Those are the primary species that we have nesting here,” said Dr. Amy Bonka, the chief conservation officer at Sea Turtle Inc.

The SpaceX launch facility is located just steps away from the dunes on Boca Chica beach, where turtles go to lay their eggs.

With all of the high altitude Starship launches ending in fireballs so far, some might wonder if nesting sea turtles are in danger from debris. 

SpaceX launches happen pretty infrequently, with only four launches since the first one in December 2020, so there may be fewer than five launches during the April to August nesting season for Kemp’s ridley sea turtles.

For the most part, the rockets have all exploded either upon the impact of landing or very shortly after they landed successfully, as with Starship SN10. Starship SN11 was different. It exploded in midair, which allowed debris to be thrown as far as Isla Blanca Park on South Padre Island.

But that’s not the usual outcome.

“Right now, no, we are not concerned,” said Bonka.

Bonka told KVEO that preliminary studies had been done on the number of turtles nesting in the nearby dunes before SpaceX even began launching rockets and that so far the launches have not had a noticeable impact.

An occasional road closure and an explosion don’t have a tremendous impact on their rescue efforts either.

“[SpaceX is] very aware of the nesting season, they’re very aware of the nesting process. They are supportive and on board, with all that we do, to patrol for nesting females and things like that,” said Bonka.

This nesting season will be different from previous ones though because this will be the first nesting season that SpaceX is conducting high altitude tests.

But the previous low altitude tests didn’t have a negative impact on the number of nesting turtles according to Bonka.

“We have seen a general increase in those numbers,” Bonka said when asked about the difference in the number of nesting turtles the past few years. “So this year we aren’t certain if the numbers will be the same or higher than what they were last year. We’re very excited to see what happens.”

If you are on South Padre Island or Boca Chica Beach and you see a nesting, stranded or injured turtle, please call Sea Turtle Inc.’s 24-hour emergency number at (956) 243-4361.

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April 09, 2021 at 10:29PM
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China drills in disputed South China Sea as US naval patrol grows - Al Jazeera English

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China has drilled deep in the South China Sea to retrieve sediment core from the seabed, state media has reported, amid tensions over disputed waters with rival claimants Taiwan and the Philippines, as the United States increases its naval presence in the region.

Chinese scientists on a marine research vessel used China’s homemade Sea Bull II drilling system to obtain a sediment core 231 metres (757 feet) long at a depth of 2,060m (6,760ft), according to the official Xinhua news agency on Thursday.

The system can help explore natural gas hydrate resources in the seabed, Xinhua added, referring to the solid ice-like crystals formed from a mixture of methane and water that are touted as a promising source of energy.

It was unclear exactly where the drilling took place in the South China Sea, approximately 90 percent of which is claimed by Beijing as its territorial waters. The International Court of Arbitration at The Hague has declared that claim as without legal basis.

Malaysia, the Philippines, Taiwan, Vietnam and Brunei also lay claim to parts of the sea, which has vast oil and gas potential.

Tensions in the region have escalated in recent weeks following revelations that 200 Chinese “maritime militia” vessels have been amassing at Whitsun Reef, about 320 kilometres (200 miles) west of Palawan Island and within the Philippines’s exclusive economic zone (EEZ).

Since then, the US has deployed a Navy strike group led by the USS Theodore Roosevelt, which entered the South China Sea on Sunday.

According to a South China Morning Post newspaper report on Friday, the US has also deployed the amphibious assault ship USS Makin Island to enter the busy sea lane through the Strait of Malacca.

The group also reportedly included the amphibious transport dock USS San Diego, the publication reported, citing information from the Beijing-based South China Sea Strategic Situation Probing Initiative.

The US has defended its latest naval activities calling it a “routine” transit and in accordance with the “freedom of navigation” principle.

On Friday, it was also reported that Chinese military vessels gave chase on Thursday to a Filipino vessel with civilians and journalists on board with the Philippines’ EEZ, according to the Manila-based television station, ABS-CBN.

‘All options open’

The Philippines, a US ally that has developed closer ties with Beijing since the administration of President Rodrigo Duterte, has voiced concern in recent days about the presence of Chinese vessels in its EEZ.

On Thursday, the Philippine defence department said it was keeping “all our options open” as Manila’s diplomatic dispute with Beijing grows.

“As the situation (in the South China Sea) evolves, we keep all our options open in managing the situation, including leveraging our partnerships with other nations such as the United States,” Philippine defence department spokesman Arsenio Andolong said on Thursday.

The Department of Foreign Affairs has also pledged to file a diplomatic protest daily until the Chinese vessels leave the Whitsun Reef.

Handout satellite imagery taken on March 23 shows Chinese vessels anchored at the Whitsun Reef within the Philippines’s’ exclusive economic zone [Handout Photo/Maxar Technologies via AFP]
Self-ruled Taiwan, which China claims as its own territory, has also threatened to shoot down Chinese drones spotted circling the Taipei-controlled Pratas Islands in the South China Sea.

In recent days, tensions in the Taiwan Straits have also grown, with the self-governing democractic island reporting on Wednesday that 15 more of the mainland’s planes crossed into Taiwan’s air defence zone.

Taipei warned that it would defend itself “to the very last day” if necessary.

On Monday the Chinese carrier, Liaoning, also led a naval exercise near Taiwan and Beijing said that such drills will become regular occurrences.

China’s oil and gas exploration activities in the South China Sea have stoked tensions before, notably when state-run China National Offshore Oil Corp (CNOOC) deployed a deepwater drilling rig in Vietnam-claimed waters in 2014.

One-third of the world’s trade estimated at more than $3 trillion passes through the South China Sea annually.

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April 09, 2021 at 09:41AM
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China drills in disputed South China Sea as US naval patrol grows - Al Jazeera English

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